B-lymphocytes, or by plasma cells (which are derived from B lymphocytes). They are also called immunoglobulins (Ig) and are of various types: IgG, IgE, IgM, IgA. The more 'typical structure and' that of IgG, consist of four polypeptide chains, two light (L) and two heavy (H), linked by disulfide bonds between cysteine residues. Each IgG molecule has the shape of a Y and the two ends 'constituted by an L chain and an H chain and that presents a region' capable of combining with other molecules (called antigens). Each IgG thus presents two binding sites for the bio x4

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